/*! \page PropertiesDoc Expectation values other than energy

Keywords: AVERAGE, DENSITY and NONLOCAL_DENSITY

\section description Description

Three groups of operators are currently implemented.
<ul>
<li>AVERAGE: this the preferred framework for evaluation of
expectation values. Results are written directly into the global
log-file that is to be post-processed with gosling to obtain
statistical error bars. AVERAGE contains both local and non-local
operators. Note that although no error/warning is generated,
the "center" estimator of a non-local operator in the \ref
Reptation_methodDoc does not correspond to the pure estimator and it
is, in general, rather useless number.
<li>DENSITY: results are written to separate files for each
operator. Only local operators are accessible via this
keyword. Evaluation of error bars is not available.
<li>NONLOCAL_DENSITY: analogous to DENSITY, but for non-local
operators. Note that these are not available (and will be ignored)
within \ref Reptation_methodDoc . As with DENSITY, evaluation of error
bars is not available.
</ul>

<p>
To evaluate an operator within a given method (VMC, DMC or RMC), include
the following line into that method's input section
</p>

<pre>
&lt;keyword> { &lt;operator> &lt;options of the selected operator> }
</pre>

<p>
For simultaneous evaluation of several operators just repeat the above
section for each operator to be evaluated.
</p>

\section options Options

Keyword: AVERAGE
<table>
<tr><th>Operator</th><th>Description</th></tr>

<tr><td>DIPOLE</td>
<td>dipole moment</td></tr>

<tr><td>SK</td>
<td>electronic \subpage Structure_factorDoc in periodic systems, useful for
estimation of Coulomb finite-size errors</td></tr>

<tr><td>GR</td>
<td>electronic pair correlation function</td></tr>

<tr><td>MANYBODY_POL</td>
<td>electric polarization</td></tr>

<tr><td>LM</td>
<td>\subpage Local_momentsDoc and local charges evaluated as integrals
of the electron density inside muffin-tin spheres</td></tr>

<tr><td>OBDM</td>
<td>\subpage OBDMDoc one-body density matrix in homogeneous and isotropic
systems</td></tr>

<tr><td>TBDM</td>
<td>projected \subpage TBDMDoc two-body density matrix in homogeneous and
isotropic systems, useful for detection of BCS-like condensates</td></tr> 

<tr><td>TBDM_BASIS</td>
<td>\subpage TBDM_BASISDoc 
</td></tr> 

<tr> <td> REGION_FLUCTUATION </td>
<td> \subpage REGION_FLUCTUATIONDoc 
</td> </tr>

</table>


Keyword: DENSITY
<table>
<tr><th>Operator</th><th>Description</th></tr>

<tr><td>DENSITY</td>
<td>\subpage One_particle_densityDoc evaluated on a 3D mesh</td></tr>

</table>


Keyword: NONLOCAL_DENSITY
<p>No operator is currently evaluated using this framework.</p>


\section related Related

\subpage Local_density_accumulatorDoc


*/
